The present invention is concerned with the color cathode-ray tube. Especially, the present invention relates to the color cathode-ray tube with the electron gun that discharges 3 electron beams at parallel in the common plane in the direction of the fluorescent face.
The color cathode-ray tube is used for television and for the monitor of the information terminal.
The color cathode-ray tube includes the following components.
(1) Electron gun at which several (3 usual) electron beams are discharged that is provided in the inside of one end of the vacuum envelope PA1 (2) Fluorescent face where several (ordinary 3 colors) fluorescent body picture elements were arranged like the mosaic applied to the inside of the other end of the vacuum envelope PA1 (3) Shadow mask that is the color selection electrode that stood and installed close to the fluorescent face PA1 (4) Deflection yoke installed in the outside of the above vacuum envelope to deflect several electron beams discharged from the above electron gun PA1 panel 1, funnel 2, neck 3, fluorescent body film 4, internal conduction film 5, shadow mask 6, mask frame 6A, mask suspension mechanism 6B, getter 7 and magnetic shield 8. PA1 deflection yoke 9, magnet 10 for the adjustment of color purity and the convergence, electron gun 11 of the in-line type, reinforcement metal fitting 12 and stem pin 13.
By scanning the electron beam to two dimensions by the magnetic field that is generated in the deflection yoke, the color cathode-ray tube displays the required image.
FIG. 3 is a perpendicular section that explains outline structure diagram of the color cathode-ray tube.
The color cathode-ray tube has the following components:
In addition, the color cathode-ray tube has the following components:
FIG. 4 is the schematic cross-sectional view that explains the structure of the electron gun of the in-line type that is used for the color cathode-ray tube of this seed. The electron gun shown in FIG. 4 has heater 20, cathode 21, the first electrode 22, the second electrode 23, the third electrode 24, the fourth electrode 25 of the anode, shield cup 26 and contact spring 27, 28 is the thing point (cross OVER). The same code as FIG. 3 corresponds to the same part.
FIG. 5 is the schematic cross-sectional view that explains the structure of the electron beam generation part of the electron gun shown in FIG. 4. The electron beam generation part shown in FIG. 5 has electron beam pass hole 22A of the first electrode 22, electron beam pass hole 23A of the second electrode 23 and electron beam pass hole 24A of the third electrode 24. 30 is the drive circuit. The same code as FIG. 4 corresponds to the same part.
The electron gun of the in-line type mounted in neck 3 in the same diagram discharges 3 electron beams EB (center beam EBc and side beam EBs.times.2) on the common plane (horizontal face). The intensity of this electron beam is modulated according to the image signal (red Sr, green Sg and blue Sb) that is applied from drive circuit 30 of the outside through stem pin 13. And then, the electron beam is deflected by the deflection magnetic field of the horizontal direction and the vertical direction that are generated in deflection yoke 9. And then, the electron beam is two-dimensionally scanned on fluorescent body film 4, and the image is regenerated.
The electron emitted from cathode 21 heated by heater 20 by 400.about.1000 V positive electric potential applied to the second electrode 23 in FIG. 4 and FIG. 5 is accelerated to the first electrode 22 side, and 3 electron beams are formed. And then, these 3 electron beams pass electron beam pass hole 22A of the first electrode 22 and pass electron beam pass hole 23A of the second electrode 23. The high voltage of 5-10 kV is applied to the third electrode 24. And then, 3 electron beams receive the focusing action a little through the pre-focus lens that is formed between the second electrode 23 and the third electrode 24. The high voltage of 20-35 kV is applied to the fourth electrode (anode) 25. And then, accelerating by the third electrode 24, 3 electron beams inject into the main lens that is formed between the third electrode 24 and the fourth electrode (anode) 25.
The electrostatic field is formed out of the electric potential difference between the third electrode 24 and the fourth electrode 25 that compose the main lens of this place. Therefore, the above electrostatic field changes the orbit of 3 electron beams EB supplied to the main lens. Therefore, 3 electron beams adjust the focus on fluorescent body film 4 respectively and form the beam spot.
By the magnetic field that is generated in deflection yoke 9 installed in the transition area of funnel 2 and neck 3 of the color cathode-ray tube, this beam spot is two-dimensionally scanned on the whole screen that is composed of the fluorescent body film. And, this beam spot is sorted for each color in the hole opening of shadow mask 6. And then, this beam spot reaches the fluorescent body of the corresponding color, and the required color image is formed.
And, in the actual operation of the color cathode-ray tube like above, the specified voltage is applied to above each electrode. It is simultaneously necessary to control the chromaticity and the brightness of the screen to display the image. By changing the drive voltage that is applied to the cathode that corresponded to each of the fluorescent body of 3 colors as it was shown in FIG. 4, the quantity of the electron beam that is emitted from each cathode is controlled synchronizing with the deflection. And, the cathodic voltage just before emitting the electron beam from the cathode is called the cathodic cutoff voltage. That is, as for this, the brightness of the screen is the voltage as of 0 levels (dark state).
In the cathode-ray tube that is generally used for color television, the diameter of the electron beam pass hole of the first electrode of the electron gun is an ordinary about 0.6 mm. And, in the cathode-ray tube that is used for the display monitor for information processing terminals such as the computer, the drive voltage is almost 50 V. And then, the electric current quantity that is emitted from the cathode at this time is an about 0.3 mA. This is equivalent to the electric current value when the screen of the above cathoderay tube is shown in recommendation brightness. This recommendation brightness is almost 100 cd/m.sup.2.
And, about the prior art of this seed, it is disclosed to the Japanese patent publication No. 53-18866 official gazette.
It is most important that in the display image of the color cathode-ray tube like above, brightness, resolution and the contrast are high. Therefore, the reduction of the beam spot diameter in the high brightness is requested, in the cathode-ray tube for the display monitor for information processing terminals such as computer from which these characteristics are required especially. And, high resolution of the fluorescent body dot pitch of each color that constitutes the fluorescent body film is required, and the increase of the number of display picture elements by expansion of the display screen is requested further.
The reduction of the diameter of the thing point that is projected and the increase of the electric current density in the cathode are valid by reducing the measure of the electron beam pass hole of the first electrode and the circumference electrode to reduce the beam spot diameter.
But generally, by the rise of Joule heat, the increase of the cathodic electric current density accelerates evaporation of electron emission materials such as the barium that constitutes the relevant cathode. Therefore, following the declination of cathodic ability, the life of the cathode-ray tube shortens it.
In addition, high resolution of the fluorescent body dot pitch and the increase of the number of display picture elements by screen expansion are connected with reduction of the beam transmission rate of the shadow mask. Therefore, the electric current quantity that is emitted from the cathode to keep screen brightness increases, and the above life shortening is accelerated more. And, it is necessary to heighten the frequency of the drive voltage that the image signal that is applied to the cathode is amplified for the increase of the number of display picture elements. This drive voltage modulates amplitude. It is normally necessary to make the clock frequency of the video band 150-200 MHz to indicate the number of picture elements of 1.3MPixel (correspondence of the 1280 dot.times.1024 line)-2MPixel (correspondence of the 1600 dot.times.1200 line). But there is a limit in the frequency characteristics of the circuit to make the amplitude of the image signal an amplification to the drive voltage.
FIG. 6A, FIG. 6B and FIG. 6C are the explanation figures of the answer characteristics of the cathodic drive voltage. The upper limit of the amplitude of the drive voltage to secure screen brightness in the video band of clock frequencies 150-200 MHz as it was shown in FIG. 6A is almost 50 V. As it was shown in FIG. 6B, delay arises in the time of the rise and the fall of the signal in 150 MHz. As it was shown in FIG. 6C,: delay arises in the time of the rise and the fall of the signal in 200 MHz, and the loss of amplitude occurs, and the input signal is deteriorated.
Therefore, the input signal is not accurately communicated to the cathode, and the reduction effect of beam spot does not appear as resolution.
That is, the indication of the vertical line that receives the influence of the horizontal deflection frequency that is relatively high frequency directly becomes difficult. That is, the phenomenon that the brightness declination of the vertical line and the bright line flow in the scanning direction occurs.
On the other hand, the drive voltage is secured about the side line that receives the influence of the vertical deflection frequency that is relatively low frequency directly. As a result the brightness difference of the vertical line and the side line increases, and the image becomes unnatural.
By low setting the cathodic voltage (that is, cathodic cutoff voltage) in the point of time when the electron begins to come out from the cathode from the drive characteristics in the cathode-ray tube, it is known that the amplitude of the drive voltage is reduced. But the beam spot diameter on the screen enlarges, and resolution is deteriorated so that in this case, the electric current density in the cathode decreases simultaneously.